Monagle et al., in U.S. Pat. No. 3,336,269, and U.S. Pat. No. 3,509,113, discuss the precipitation process for the manufacture of polyacrylamides from a solvent mixture of acetone-water or tert. butanol-acetone-water. The invention disclose that, as known in the art, free radical polymerization reactions are carried out in the substantial absence of oxygen which is accomplished by nitrogen displacement. They also indicate that, although such reactions can occur in the absence of a polymerization initiator, such an initiation is preferred; with 0.05 to 0.2% of initiator as the preferred concentration.
Kim, in U.S. Pat. No. 3,872,063, discloses the aqueous polymerization of acrylic acid type monomers with a sorbitol or equivalent bisulfite polymerization catalyst in an inert atmosphere such as in argon or nitrogen for from 0.5 to 25 hours to manufacture a polymer of about 6 million apparent molecular weight.
Volk and Hamlin, in U.S. Pat. No. 3,658,772 also disclose the aqueous polymerization of acrylic acid type monomers. In this patent the products are copolymers of acrylic acid and acrylamide manufactured in aqueous solution in the presence of a free-radical polymerization initiator at about pH 1 to about pH 3.2. The pH of the solution is said to be critical to the success of the reaction.
Glavis, in U.S. Pat. No. 3,058,958, discloses the polymerization of sodium and calcium salts of acrylic acid on a heated surface of at least above 100.degree. C.
Ballast, in U.S. Pat. No. 3,509,114, claims the polymerization of acrylic monomers in aqueous solution containing at least 1% of an alkali metal chloride.
None of the cited references provide a method of manufacturing a linear acrylic acid polymer of over 20,000,000 molecular weight.